In the desalination of ionogenic solution with the aid of the electrodialysis there are arranged cation and anion exchanger diaphragms in alternating sequence between two electrodes in such a way that there develop between the diaphragms, in each case, closed chambers. Through the application of an electric field between the electrodes the anions migrate in direction toward the anode, and the cations in direction of the cathode. The anions can hereby pass the positively charged anion exchanger diaphragm, but are held back by the cation exchanger diaphragm. The cations migrating to the cathode pass the negatively charged cation exchanger diaphragm, but are held back by the anion exchanger diaphragm. Through this there result alternating chambers in which takes place a salt enrichment (concentration) and a desalination. In the practical application of electrodialysis the individual cells are continuously flushed with a diluted and a concentrated solution. For the economical operation of the process it is however of particular importance that the velocities of flow in the two cells are as uniform as possible so that there cannot occur a concentration polarization on the diaphragm surfaces. Furthermore, any passage of the concentrated solution into the diluted solution through leaks into the chambers separated through the ion exchanger diaphragms must be prevented. For this reason the design of the chambers presents quite a considerable problem in the construction of an electrodialysis unit. On most of the currently used electrodialysis units the diaphragms are always separated from each other by a frame of plastic material. These plastic frames are provided with perforations for the supply of the desalinated and the concentrated solution. The diaphragms are mechanically sealed on the frames. Since the individual chambers for the concentrated and desalinated solution are alternatingly arranged in one cell assembly, it is necessary that the supply of the concentrate or of the desalinated solution, respectively, likewise takes place alternating into the cell.
In general the flow approach of a cell occurs diagonally in a corner of the cell, and the withdrawal of the solution takes place at the opposite side of the cell so that the flow of the concentrate and of the desalinated solution is guided exactly contrarily on both sides of the diaphragm. This causes that the flow distribution in the chambers is not optimal and that there develop zones of low intermixture and thus increased concentration polarization. In addition, as a result of the differing flow approach the pressure drops in the chambers with the concentrated and the desalinated solution are not always equal and this causes pressure differences between the cells. This results in an additional load on the diaphragm and possibly a change of the geometry of the cell. Furthermore, in case of a mechanical sealing of the diaphragms of usually rough surface there frequently occur leaks which can cause an escape of the solution from the concentrated one into the desalinated solution. All these effects considerably affect the economy of the process.